Switching device for transformers having stepwise voltage control under load

ABSTRACT

A switching device for transformers having stepwise voltage control under load and employed for maintaining a specified level of the output voltage of electric stations and sub-stations, wherein one diagonal of a bridge circuit formed by four switching members includes a load switch, and the other diagonal has included therein the movable contacts of a selector switch associated with the leads of the winding of the transformer, connected in series with a resistor for limiting the current appearing during a switching-over operation, when the controllable output lead of the transformer is connected simultaneously with a pair of the leads of the transformer winding. The switching members and the load switch are so operated, that throughout a switching-over operation the load current of the transformer is continuous, and the switching over of all the currents is effected by the load switch.

llited States Patent [1 1 Krasov [451 Sept. 25, 11973 SWITCHING DEVICE-FOR TRANSFORMERS HAVING STEPWISE VOLTAGE CONTROL UNDER LOAD [76] Inventor: Alexandr Ivanovich Krasov, ulitsa Schastlivaya, 7b, kv.26, Zaporozhie, U.S.S.R.

221 Filed: July 7, 1972 211 Appl. No.: 269,808

Primary Examiner-A. D. Pellinen Att0rney-John C. Holman et a1.

[5 7] ABSTRACT A switching device for transformers having stepwise voltage control under load and employed for maintaining a specified level of the output voltage of electric stations and sub-stations, wherein one diagonal of a bridge circuit formed by four switching members includes a load switch, and the other diagonal has included therein the movable contacts of a selector switch associated with the leads of the winding of the transformer, connected in series with a resistor for limiting the current appearing during a switching-over operation, when the controllable output lead of the transformer is connected simultaneously with a pair of the leads of the transformer winding. The switching members and the load switch are so operated, that throughout a switching-over operation the load current of the transformer is continuous, and the switching over of all the currents is effected by the load switch.

2 Claims, 2 Drawing Figures PAIENTEusmsms l I DRIVING MECHANISM INTERRUPTER 7,,

BACKGROUND OF THE INVENTION The present invention relates to electric apparatus for transformers, and, more particularly, it relates to switching devices for transformers having stepwise voltage control under load.

Known in the art are switching devices for transformers having stepwise voltage control under load, incorporating a bridge circuit into which the switching members are connected.

The known switching device for transformers having stepwise voltage control under load comprises four load-switching means connected into a bridge circuit, a resistor for limiting the voltage appearing during a switching-over operation, when the controllable output lead of the transformer is connected at the same time with two of the leads of the transformer winding. The resistor is included into one diagonal of the bridge circuit, while a selector switch associated with the leads of the transformer winding and including stationary contacts and movable ones is connected into the other diagonal of the bridge circuit.

A disadvantage of this known switching device for transformers is the fact that it includes four load switching means, which complicates the structure of the device.

Another disadvantage of the known switching device is the fact that the electric insulation of each one of the four load switching means should be rated to the test voltage of the voltage control stage of the transformer, determined by taking into consideration the values of the over-voltage (owing to atmospheric conditions, switching periods, etc.) that might appear across the transformer winding in operation.

SUMMARY OF THE INVENTION In accordance with the above, it is an object of the present invention to simplify the structure of the switching device by reducing the number of the load switching means.

It is another object of the present invention to make the structure of the device free from members that must have electric insulation rated for the test voltage of the voltage control stage of the transformer.

It is yet another object of the present invention to increase the reliability of the performance of the switching device for transformers.

With these and other objects in view, the present invention resides in a switching device for transformers having stepwise voltage control under load, incorporat-- ing a bridge circuit and having the contacts of a selector switch associated with the leads of the transformer winding connected with a load switching means and a resistor for limiting the current appearing during a switching-over operation, when the output lead of the transformer is connected at the same time with two of the leads of said transformer winding, in which device, in accordance with the invention, the current limiting resistor is connected in series with the movable contacts of the selector switch into one diagonal of the bridge circuit formed by the switching members, while the load switching means is connected into the other diagonal of the bridge circuit, the switching members and the load switching means being so operated, that throughout a switching-over operation the load current of the transformer is continuous, and the switching of all the currents is effected by the load switching means.

It is expedient that the switching device should have all the movable contacts of the selector switch, associated with the leads of the transformer winding, connected through the stationary contacts to one lead of the transformer winding.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects and advantages of the present invention will become apparent from the following description of an embodiment of the present invention, with reference being had to the appended drawings, wherein:

FIG. 1 is the circuit diagram of the switching device for transformers having stepwise voltage control under load, in accordance with the invention;

FIG. 2 is the diagram of the same switching device including controllable diodes as the load switching means, in accordance with the invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT Refering now to the appended drawings, the circuit diagram of the switching device is illustrated in FIG. 1. The switching device for transformers having stepwise voltage control under load includes four switching members in the form of contacts 1, 2, 3 and 4, connected into a bridge circuit, a resistor 5 included into the first diagonal of the bridge circuit, one lead of the resistor 5 being connected to the contacts 3 and 4 and the other lead thereof being connected to a movable contact 6, and an interrupter 7 for switching the load, included into the other diagonal of the abovementioned bridge circuit. In the first diagonal of the bridge circuit the contacts 1 and 2 have connected thereto a second movable contact 8 which, together with the first movable contact 6, is associated with one of the leads of the transformer winding through a stationary contact 9.

The diagram of the same switching device, including controllable diodes as the load switching means, is illustrated in FIG. 2. An actuating mechanism 10 is connected with a shaft 11 having discs 12, 13, 14 rigidly mounted thereon, the discs 12 and 13 having a semicircular shape and being so mounted on the shaft that their planes are perpendicular to the shaft and are turned through relative to each other and the disc 14 is in the form of two segments extending in a plane perpendicular to the shaft 11 and turned through 180 in relation to each other. The discs 12 and 13 together with the contacts 4, 3, and 1, 2 form four switching elements connected into the bridge circuit. The interrupter 7 includes thyristors 15 and 16, diodes 17 and 18 and a control element formed by contacts 19 and 20 together with the disc 14. The thyristor l5 and the diode 18 have the positive leads thereof connected to the negative lead of the thyristor 16 and are connected to the contacts 2 and 4. The positive leads of the thyristor 16 and of the diode 17, as well as the negative lead of the thyristor 15 are connected to the contacts 1 and 3. The negative lead of the diode 17 is connected to the control lead of the thyristor 15 and to the contact 20, while the negative lead of the diode 18 together with the control lead of the thyristor 16 is connected to the contact 19. The shaft 11 further carries thereon a pair of arms 21 and 22 of which the planes extend at right angles to the shaft, the arm 22 being rigidly secured to the shaft and the arm 21 being connected to the shaft through a positive play coupling 23. The arms 21 and 22 are asociated, respectively, with a pair of Geneva crosses 24 and 25 mounted on the respective shafts 26 and 27 that are parallel to the shaft 11. The shafts 26 and 27 are coupled, respectively, with the abovementioned movable contacts 6 and 8 that are adapted to engage six stationary contacts 9, 28, 29, 30, 31 and 32 arranged in circles concentric with the shafts 26 and 27, respectively. The stationary contacts are connected with the six respective leads of the winding 33 of the transformer. The stationary and movable contacts 6, 8, 9, 28, 29, 30, 31 and 32 together with the shafts 26 and 27, the Geneva crosses 24 and 25 and the arms 21 and 22 constitute a transformer winding lead switching device 34.

The switching device operates, as follows. In the static state of the device, i.e., in the state between successive switching operations, the shaft 1 1 is not rotated, and the load current I which flows through the controllable winding of the transformer, also flows through contacts 1 and 8 that are the main contacts and are intended for prolonged passage of the load current I,,. The contacts 2, 3 and 4, 6 have no current flowing therethrough in the static condition of the device, and, therefore, they are auxiliary contacts.

The switching device is operated by rotation of the shaft 1 1 from the actuator 10. The operation of switching the load of the transformer from one lead of the controllable winding 33 of the transformer, e.g., from the lead associated with the contacts 9 to another lead, e.g., the one associated with the contacts 28, can be divided into several successive stages.

With the shaft 11 being rotated, the contacts 12 and 13 engage the contacts 3 and 2, respectively, while the contacts 1 and 4 also remain closed for a certain period. The disc 14 establishes connection between the contacts 19 and 20. After the shaft has been rotated through an angle corresponding to the angular extent of the contact 1, the contacts 1 and 4 break, and the load current starts flowing through the thyristors l and 16, because, with the contacts 19 and 20 having been closed, opening signals are fed to the control leads of the thyristors 15 and 16. The contacts 19 and 20 break after the shaft 11 has been further rotated through an angle corresponding to one half of the angular extent of the segment of the disc 14, whereby the control circuit of the thyristors 15 and 16 becomes broken. Consequently, the load current 1,, flows no longer through these thyristors and flows instead through the contact 3, the current-limiting resistor 5, the movable contact 6 and the stationary contact 9 into the winding 33 of the transformer.

In such a way, at this stage the load current 1,, does not flow through the movable contact 8, and thus the latter can be shifted from the stationary contact 9 to the adjacent stationary contact 28. The shifting is effected with the help of the arm 22, the Geneva cross and the shaft 27. This shifting is not accompanied by shifting of the movable contact 6, because the arm 21 transmitting rotation to the Geneva cross 24 and the shaft 26 is connected to the shaft 11 not rigidly, but through the positive play coupling 23, whereby the arm 21 lags behind by an angle equal to one half of the angular play of the coupling 23. After the movable contact 8 has been shifted, the contacts 1 and 4 close, and the contacts 19 and 20 make, too, whereby the load current starts flowing through the contact 1, the movable contact 8 and the stationary contact 28 into the winding 33 of the transformer. There is also a current flowing between the stationary contacts 9 and 28, the value of this current being defined by the voltage of the respective control stage (i.e., the voltage across the contacts 9 and 28) and by the resistance of the resistor 5. The last-mentioned current flows through the stationary contact 9, the movable contact 6, the resistor 5, the contact 3 that has not yet been disengaged, the contact 1, the movable contact 8 and the stationary contact 28. With the shaft 11 being rotated further on, the contacts 2 and 3 break, and the current between the contacts 9 and 28 starts flowing through the tyristors l5 and 16.

With the shaft 11 being further rotated, the contacts 19 and 20 break, the current through the thyristors l5 and 16 ceases, and, therefore, the current flowing through the contacts 9 and 6 is discontinued, too. No current flows now through the movable contact 6, and thus it becomes possible to shift the contact 6 from the stationary contAct 9 to the stationary contact 28. The last-mentioned shifting is effected with the help of the arm 21, the Geneva cross 24 and the shaft 26. Now the operation of switching over the load from the stationary contact 9 to the stationary contact 28 is completed.

Switching over of the load from the stationary con tact 28 to the stationary contact 29 and vice versa is effected in a similar manner. During the switching operation the thyristors l5 and 16 are operated so that the current being switched off would not rise above the load current I,,, while the voltage pressure across the thyristors 15 and 16 after the load current has been switched off would not be in excess of the control stage voltage, provided that the resistance of the currentlimiting resistor 5 is equal to the control stage voltage U,," divided by the load current I,,, e.g.,

R ni n where R is the ohmic resistance of the resistor 5;

U,, is the control voltage stage, Volts;

l,," is the load current, Amperes.

The herein disclosed switching device is intended for use in association with transformers having stepwise voltage control under load, employed for maintaining a specified level of the voltage supplied by electric stations and transformer sub-stations.

The employment of the herein disclosed device makes it possible to reduce the size of the transformers, to cut down their cost and to increase their reliability.

What we claim is:

l. A switching device for association with transformers adapted for stepwise voltage control under load, comprising: four switching members connected into a bridge circuit and adapted to effect a desired succession of the operation of switching over from one lead of the winding of the associated transformer to another such lead; load switching means connected into one diagonal of said bridge circuit formed by said switching members; a selector switch associated with said leads of said winding of said transformer, including stationary contacts connected to the respective ones of said winding leads and at least two movable contacts, said selector switch being adapted to control said load switching means and said switching members; a resistor means being so operated, that the load current of said transformer is continuous throughout a switching-over operation, and the switching over of all the currents is effected by said load switching means.

2. A switching device as set forth in claim 1, wherein all said movable contacts of said selector switch associated with said leads of said winding of said transformer are connected through said stationary contacts to one lead of said winding of said transformer. 

1. A switching device for association with transformers adapted for stepwise voltage control under load, comprising: four switching members connected into a bridge circuit and adapted to effect a desired succession of the operation of switching over from one lead of the winding of the associated transformer to another such lead; load switching means connected into one diagonal of said bridge circuit formed by said switching members; a selector switch associated with said leads of said winding of said transformer, including stationary contacts connected to the respective ones of said winding leads and at least two movable contacts, said selector switch being adapted to control said load switching means and said switching members; a resistor for limiting the current appearing at the switching-over period, when the controlable output lead of said transformer is connected simultaneously with a pair of said leads of said winding of said transformer, said resistor being included into the other diagonal of said bridge circuit formed by said switching members, in series with said movable contacts of said selector switch associated with said leads of said winding of said transformer; said switching members and said load switching means being so operated, that the load current of said transformer is continuous throughout a switching-over operation, and the switching over of all the currents is effected by said load switching means.
 2. A switching device as set forth in claim 1, wherein all said movable contacts of said selector switch associated with said leads of said winding of said transformer are connected through said stationary contacts to one lead of said winding of said transformer. 